Imaging, communication, and spectroscopic applications in the mid- and far-infrared regions have underscored the importance of developing reliable sources and detectors operating in the frequency range from 0.1 to 100 THz (3000 to 3 μm wavelength). Recent studies, such as T-Ray Imaging by D. Mittleman et al. in IEEE Journal of Selected Topics in Quantum Electronics vol. 2 1996 and TeraHertz Technology by P. Siegel in IEEE Transactions on Microwave Theory and Techniques vol. 50 2002, suggest that terahertz interactions can enable a variety of new applications on a wide range of solids, liquids, gases, including polymers and biological materials such as proteins and tissues.
For example, the resonant frequencies of many rotational and stretching transitions in complex organic molecules, such as proteins, are in this frequency range. Also, phonon energies of polar molecules may be in this range. Thus, THz frequency radiation sources may find significant uses in the fields of spectroscopic analysis and/or photochemical processes involving these molecules.
Compared to microwave devices, devices operating in the THz, or far-infrared, frequency range may allow significant reductions in antenna size, as well as providing greater communication bandwidth. Additionally, the shorter wavelength of THz frequency waves, compared to microwaves, allows greater resolution with THz frequency waves than is possible with microwaves. Commercial applications may include thermal imaging, remote chemical sensing, molecular spectroscopy, medical diagnosis, fire and combustion control, surveillance, and vehicle driver vision enhancement. Military applications may include night vision, rifle sight enhancement, missile tracking, space-based surveillance, and target recognition.
THz frequency radiation has also reported from silicon-based quantum well structures by G. Dehlinger et al. in Intersubband Electroluminescence from Silicon-Based Quantum Cascade Structures, Science, vol. 290, Dec. 22, 2000. These silicon-based quantum cascade devices disclosed to provide electroluminescence in the THz frequency band with a minimum bandwidth of about 1.8 μm.
Electrically pumped non-quantum well THz emitters and detectors with relatively broad bandwidths (>10 μm for radiation in the range of about 20 μm to 60 μm) were disclosed in a U.S. patent application by J. Kolodzey et al. entitled TERAHERTZ FREQUENCY RADIATION SOURCES AND DETECTORS BASED ON GROUP IV MATERIALS AND METHOD OF MANUFACTURE filed on Apr. 7, 2004. This U.S. patent application claims priority from U.S. Provisional Application No. 60/461,656, as does the present application, and is incorporated by reference herein. The broad bandwidth THz emitters disclosed therein provide improved efficiency over the quantum well and optically-pumped examples described above.
Such wide bandwidth devices may have many uses, but in some applications narrower bandwidth THz emitters and/or detectors may be desirable. For example, in thermal imaging, remote chemical sensing, molecular spectroscopy, medical diagnosis, fire and combustion control, surveillance, and target recognition applications, quick initial screening using one or more narrow wavelength bands within the THz range may be desirable. One method to create a narrow bandwidth THz emitter may be to produce a THz frequency laser using a broader bandwidth gain material, such as those described above. This method does not address the creation of a possible narrow bandwidth THz detector, though.